Tens of millions of children in the United States co-reside with pet dogs. Recent research suggests living or interacting with dogs promotes learning outcomes and has health benefits. Biological mechanisms underlying these processes are largely unknown but may include protective effects on the activity of stress-sensitive biological systems. The neuroendocrine arm of the stress system known as the hypothalamic-pituitary- adrenocortical (HPA) axis may be of particular importance because 1) it influences long-term neural activity and many organ systems, 2) disturbances in it are linked with impaired cognitive and emotional functioning and a range of physical diseases across the lifespan, and 3) its activity is impacted by diverse qualities of human social relationships. Among infants and children, supportive relationships with close family members have a buffering effect on HPA axis activity in response to stress. Along with family members and close friends, pet dogs are known confidantes for children. It is unknown whether pet dogs buffer the HPA response to stress. We propose testing the stress-buffering potential of pet dogs in a standardized laboratory protocol, the Trier Social Stress Test, known to produce reliable stress responses in children and adults. 90 nine-year-old children from dog-owning families will be tested either in the presence of their dog, their parent, or without a support figure. To date there are no studies testing individual differences in the child, pet, or child-pet relationship that impact the degree to which pet dogs confer health benefits (stress-reducing or otherwise) for children. Thus we further aim to examine characteristics that moderate dogs' impact on children's stress responses. We hypothesize that the presence of a pet dog during a laboratory-based social stressor will buffer the child's biological response to the stress test, and that this buffering will be similar to that observed in the presence of a support person - the parent. We further hypothesize that across experimental conditions, the buffering effect will be impacted by the child's temperament and attachment to the dog as well as the dog's sociability and responsiveness to the child's gestures. By characterizing the role of pet ownership and pet presence in the developing biological stress response in children, the results obtained will contribute both to our understanding of stress in children and how it can be buffered, and also to our understanding of how human-animal interaction may have health benefits. Thus the outcome of this project will be a better basis for the burgeoning field of animal interactive therapy.